Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2001-02-21
2003-03-18
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S326000, C430S330000, C427S097100, C428S209000, C428S901000
Reexamination Certificate
active
06534245
ABSTRACT:
TECHNICAL FIELD
The present invention is concerned with providing an aperture filling layer supported on a carrier film and with filling apertures in a circuit board or chip carrier with dielectric material. The present invention provides particular applicability in filling plated through holes in integrated circuit boards or chip carriers. In addition, the present invention provides for achieving a planar top surface along with the filling of the apertures. This can be accomplished by the present invention without causing dimensional changes or adversely impacting the dimensional stability of the printed circuit board.
BACKGROUND OF INVENTION
Substrates on which an electronic device are electrically mounted are commonly fabricated from dielectric materials such as ceramics, ceramic metal composites, polymeric materials and polymeric material-metal composites. These substrates can have multi-level electrical conductor patterns embedded therein.
In the simplest embodiments, the substrate has one dielectric layer having electrical conductor patterns on both sides thereof which are electrically interconnected by a plurality of electrically conducting apertures or vias extending through the substrate.
In an alternative embodiment, the substrate is fabricated from an electrically and/or thermally conducting layer coated with a dielectric material. A plurality of through-holes are drilled, punched or etched through the substrate. To form an electrically conducting aperture or via which is electrically isolated from the core, the through-holes are typically plated with an electrically conductive layer and then filled at least in the region of the core with an electrically insulating material.
However, the techniques employed for filling the vias require subsequent planarization so as to ensure that the surfaces are planar whereby the dielectric is flush or level with the metallization thereon. However, various of these prior art planarization methods introduce dimensional changes to the printed circuit board or adversely impact its dimensional stability. Planarization is normally done by belt-sanding and/or chemical polishing method which include mechanical deformation or stretching to the printed circuit board. Such dimensional changes affect subsequent circuitization processes.
Accordingly, continuing efforts are underway for providing improved techniques for filling apertures in printed circuit boards.
SUMMARY OF INVENTION
The present invention provides a photosensitive dielectric on a film carrier, and a process for filling apertures in a printed circuit board or chip carrier with such dielectric material that overcomes problems present with current techniques. More particularly, the present invention provides a process for filling apertures in a circuit board or chip carrier with a dielectric material along with the ability to achieve a planar surface that avoids introducing dimensional changes and does not adversely impact the dimensional stability of the printed circuit board or chip carrier.
More particularly, one aspect of the present invention is concerned with a process of filling apertures in a printed circuit board or chip carrier with a cured photosensitive dielectric material which comprises substantially filling the apertures in the circuit board with a positive photosensitive dielectric material and providing a layer having a thickness of the positive photosensitive dielectric material on the circuit board or chip carrier. The photosensitive dielectric material is then exposed to radiation of an intensity and for a duration of time effective for causing the photosensitive dielectric material to be exposed to a depth of substantially the thickness provided on the circuit board or chip carrier but leaving the photosensitive material located in the apertures unexposed. The photosensitive dielectric material is subjected to baking at elevated temperatures in order to cure the unexposed material located in the apertures, and the exposed photosensitive dielectric material is developed and removed thereby leaving behind cured photosensitive dielectric material in the apertures. The baking can occur prior to and/or after the developing of the exposed photoresist. Also, the baking can be such that partial cure occurs prior to the developing with the final cure occurring after developing.
According to a further aspect of the present invention, apertures in a printed circuit board or chip carrier are substantially filled along with providing a layer having a thickness to the printed circuit board with a positive photosensitive dielectric material. The photosensitive dielectric material is selectively exposed to radiation except for photosensitive dielectric material located within the vicinity of apertures thereby leaving photosensitive dielectric material located within apertures unexposed. The photosensitive dielectric material is baked to thereby cure the unexposed portions of the photosensitive dielectric material and the exposed photosensitive dielectric material is developed thereby removing it while leaving behind cured photosensitive dielectric material in apertures. The baking can be carried out prior to and/or after the developing of the exposed photoresist. Also, the baking can be carried out so that partial cure occurs prior to the developing and final cure occurs after the developing.
The present invention also relates to chip carriers and circuit boards with holes filled according to the above processes.
Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described only the preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature and not as restrictive.
BEST AND VARIOUS MODES FOR CARRYING OUT INVENTION
The present invention relates to filling apertures in a circuit board or chip carrier with a dielectric material. More particularly, the present invention includes filling apertures in a circuit board or chip carrier with a positive photosensitive dielectric material. According to the present invention, this can be accomplished by such techniques as coating, screening or stenciling the desired amount of a flowable positive photosensitive dielectric material to fill the apertures and the surrounding area of the apertures on the surface of the circuit board or chip carrier. The photoresist material employed typically is tack free at normal room temperatures and flowable at temperatures of about 180° C. or lower, and more typically at temperatures of about 50° C. to about 160° C. Moreover, typically the photosensitive dielectric material has viscosity of about 20,000 to about 1,000,000 and more typically about 20,000 to about 500,000 cps.
If aqueous alkaline development is desired, the light sensitive composition according to the invention can contain components for example a polyphenol or a mixture of polyphenols, i.e. a polymer having a specific content of phenolic hydroxyl groups. This content should at least be sufficiently high to ensure development, or at least swelling, in an aqueous alkaline solution of developer.
Suitable film-forming components soluble in aqueous alkaline solutions can be classified in the following groups:
novolaks formed from at least one phenol and at least one aldehyde,
homopolymers and copolymers of alkenylphenols and, in particular,
homopolymers and copolymers of N-hydroxy-phenylmaleinimides.
Preferred novolaks are compounds derived from a C
1
-C
6
aldehyde, for example formaldehyde and acetaldehyde, and from a mononuclear, substituted or unsubstituted phenol. Examples of preferred phenols are phenol itself or phenols substituted by one or two C
1
-C
9
alkyl groups
Appelt Bernd Karl
Johansson Gary Alan
Papathomas Konstantinos I.
Barreca Nicole
Connolly Bove & Lodge & Hutz LLP
Fraley Lawrence R.
Huff Mark F.
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